Formation of fins on metal bar or tube stock



June 23, 1964 J ow ETAL 3,137,926

FORMATION OF FINS ON METAL BAR OR TUBE STOCK Filed March 51, 1958 4Sheets-Sheet l INVENTORS Jean 8- Bnkmw FRRNK E. Mari-IN Gemzaa T- MAWMN'm mng E. CHAPMAN Enema w. DRLBY BY M Mia av June 23, 1 4 J. A. BARLOWETAL FORMATION OF FINS 0N METAL BAR OR TUBE STOCK 4 Sheeis-Sheet 2 FiledMarch 31, 1958 He. 5 p.

INVENTORS Joe-m A. Baku-ow FRnNK E. MAR-rm. Game; 1'- Mus-MN. Thomas E.CMRPMAN. Emma N. put BY .1

' A'r'romeY FIG. 5B.

June 23, 1964 4 J. A. BARLOW ETAL 3,137,926

FORMATION OF FINS ON METAL BAR OR TUBE STOCK Filed March a1, 1958 4Sheets-Sheet 5 INV TORS JOHN BRRl-OW FRANK E. MARTI GEORGE T. A BH N mas5.cum maan: H. DALBY.

ATTORNEY June 23, 1964 J. A. BARLOW ETAL 3,137,926

FORMATION OF FINS ON METAL BAR OR TUBE STOCK Filed March 31, 1958 4Sheets-Sheet 4 INVENTORS Jmm A. Bmusw Fmmx E. manna 6:025; T. mauaumTpqgmAS 'Eu MPMRN Eur-Ag w. Din.

ATTORN EY United States Patent 3,137,926 FORMATION OF FKLJS ON METAL BARQR TUBE STUCK John Alfred Barlow, Frank Edward Martin, George ThomasMaugham, Thomas Edwin (Ihapman, and

Edgar William Dalby, all of Hayes, England, assignors,

by mesne assignments, to Fairey Engineering Limited,

Heston, Engiand, a company of Great Britain Filed Mar. 31, 1958, Ser.No. 725,198 Claims priority, application Great Britain Apr. 2, 1957 2Claims. (Cl. 29-1575) This invention relates to the forming of anintegral protruding fin on a workpiece and is particularly although notexclusively applicable to the formation of an integral external fin onmetal stock of cylindrical bar or tubular form.

It is known to roll a thread on a metal bar using a number ofsmall-diameter, rotatable discs freely mounted on a spindle by means ofwhich the edges of the discs are pressed against the side of the slowlyrotating bar. A similar method, using freely mounted discs ofcorrespondingly larger radius, has been tried by the applicants forrolling thin, deep fins on bar or tube stock but was found unsuccessful.

According to the present invention a process of forming an integral finon the surface of a workpiece made of a material which when heatedbecomes softened and capable of being extruded, includes pushing intocontact with the workpiece surface a tool whose workpiece-engaging partsinclude a pair of spaced, generally parallel edges which are moving athigh speed relatively to the workpiece in the direction of their lengthsand substantially tangentially to the workpiece surface, the edges beingseparated by an elongated gap, so as to cause local heating andsoftening of the material of the workpiece and to displace the softenedmaterial outwardly into the gap to form a fin protruding beyond theoriginal surface of the workpiece. The tool may be traversed slowlyrelatively to the workpiece surface whilst being pressed against it, ina direction generally parallel to the direction of movement of the edgesat their region of contact with the workpiece.

In one form of the invention the tool is rotatably mounted and isrotated at high speed, and the workpieceengaging edges respectivelyinclude portions lying along or at a small angle of inclination to acircle coaxial with the axis of rotation of the tool.

Thus in one arrangement the tool may include two or more coaxial discsor annular flanges or'rings whose outer peripheral margins are spacedapart and afford the workpiece-engaging edges of the tool.

For forming a continuous helical fin extending coaxially around aworkpiece of cylindrical form the latter may be slowly rotated Whilstthe tool is traversed along the length of the workpiece. In this casethe axis of rotation of the tool should preferably be inclined to theaxis of the workpiece at an angle corresponding to the angle of lead ofthe helix.

The tool may include a milling cutter mounted behind the rotating edgesin a position in which it will enter the groove between the adjacentconvolutions of the helical fin to trim the base of the groove.

Similarly, circumferential or longitudinal fins may be formed byappropriately traversing the tool relatively to the workpiece surface.

In the one arrangement of the invention the tool may include a number nof workpiece-engaging rotary edges, where n is greater than 2, so thatn1 fins are formed simultaneously.

According to a further feature of the invention two or more of thespaced workpiece-engaging edges of the tool are each comprised of one ormore blunt leading hce edge portions each inclined to its own path oftravel at a small angle in a direction rearwardly and away from thetool, so that the rotating tool delivers a series of impacts to theworkpiece. Thus where the members comprise spaced coaxial discs, atleast one pair of the discs may be formed with radial undulationsextending around with the workpiece.

their peripheries. Alternatively the discs may each be formed with oneor more outwardly protruding peripheral lugs, each lug affording arearwardly inclined leading edge oblique to the direction of travel forengagement Again, the edge of each disc may be generally circular butformed with one or more flats for impact engagement with the workpiece.

In another form of the invention the members instead of being discs maytake the form of thin spaced coaxial rings or flanges which surround theworkpiece and are rotated at high speed about their common axis, thegenerally circular inner edges of the rings or flanges being pressedinto engagement with the side of the workpiece to form circumferentialor helical fins by outward displacement of the metal between the narrowannular spaces between the rings. The edges of the rings may be formedwith undulations projections, discontinuities or other variations intheir radial heights to afford impact portions as mentioned above. Therings may all be mounted within a common drum which is rotated about itsaxis and is moved transversely relatively to the workpiece to effectengagement of the rings with the workpiece.

The invention according to another of its aspects comprises apparatusfor forming an integral fin by the method referred to on a materialwhich when heated softens and is capable of being extruded, whichcomprises means for supporting the workpiece, a tool-holder carrying atool having at least two spaced, generally parallel blunt edgesseparated by an elongated gap, means for moving the edges longitudinallyat high speed relatively to the workpiece and means for advancing thetool to press the mov-: ing edges generally tangentially against thesurface of the workpiece.

For example the apparatus may comprise a lathe, a tool-holder mounted onthe cross-slide of the lathe, a tool mounted in the tool-holder andcomprising a number of close-spaced coaxial rotary members havinggenerally circular edges defining between them one or more narrow gapsdriving means for rotating the members about their common axis at a highspeed, means for moving the tool-holder in such a manner as to press theedges of the rotating members into the surface of the workpiece, andmeans for traversing the tool-holder to move the edges relatively to theworkpiece surface in a direction generally transverse to the axis ofrotation of the members whilst they are pressed against the workpiece.

The invention according to another aspect comprises a length of bar ortube formed with at least one integral external fin by the methodreferred to.

The invention may be carried into practice in various ways, but certainspecific embodiments will now be described by way of example withreference to the accompanying drawings in which:

FIGURE 1 is a perspective view of apparatus for forming a continuoushelical fin on a tubular metal workpiece,

FIGURE 2 is a diagram illustrating how the workpiece is set up in theapparatus, and how the fin is formed to. project beyond the originalworkpiece surface,

FIGURE 3 is a view showing diagrammatically the profile of a typicaldisc used in the apparatus of FIG- URE 1,

FIGURE 4 is a sectional diagrammatic view of a train of two discs and acutter used for forming a single helical fin,

FIGURES 5A and 5D illustrate various modified forms of disc havingdifferent profiles,

FIGURE 6 is a perspective view similar to FIGURE 1 of a modifiedembodiment for forming a longitudinal fin,

FIGURE 7 is a perspective view of part of another modified embodimentemploying rotating rings instead of discs,

FIGURE 8 is an end view of the cage and rings of the embodiment ofFIGURE 7, and

FIGURE 9 is a section on line IXIX of FIGURE 8,

In the embodiment of FIGURES 1 to 5, the invention is applied to theformation of a continuous helical fin on a workpiece consisting of alength of cylindrical bar or tubular stock of light alloy, for exampleof magnesiumberyllium alloy.

The tubular workpiece 10 is mounted between the headstock 11 andtailstock 12 of a screw-cutting capstan lathe 13 as shown in FIGURE 1.The two end portions 14 and 15 of the workpiece 10 are turned down to asmaller diameter than that of the original workpiece which is indicatedat 16 in FIGURE 2. At the headstock end the workpiece end 14 is slottedat 17 (FIGURE 2), and the spigot 18 of a centrepiece 19, is inserted inthe end of the workpiece and is provided with a transverse driving pin20 which engages in the slot 17 of the end 14 of the workpiece. Thecentrepiece 19 is mounted in the chuck 21 of the headstock 11 so thatthe workpiece will be rotated by the chuck.

At the other end 15 the workpiece is also provided with a centrepiece 22which is journalled in a roller race 23 carried by the tailstock 12 soas to support the rotating end 15 of the workpiece.

Mounted on the cross-slide 24 of the lathe is a supporting structure 25on top of which is mounted an electric motor 26. The structure 25 alsocarries a downwardly depending bearing tongue 27 and a bearing block 28in which are journalled the ends of a spindle 29. A pair of coaxialdiscs 30 and a milling cutter 31 are rigidly mounted on the spindle 29for rotation therewith and the spindle is driven at high speed by themotor 26 through a belt drive 32. The spindle axis is slightly above andto one side of the axis of the workpiece, so that by transverse movementof the cross-slide 24 the edges of the rotating discs can be advancedinto contact with the edge of the workpiece. As illustrated in FIGURE 3,each of the discs 30 has its edge of smoothly undulating form, affordinga series of radially projecting portions or radial projections 32 eachof which has a smooth leading edge 33 backwardly inclined rearwardly andoutwardly with respect to the direction of travel of the edge, theportions 32 thus constituting impact members whose leading blunt impactfaces 33 will engage the metal of the workpiece with a hammer effectwhen the rapidly rotating discs 30 are pressed into the surface of theworkpiece. The peripheral margins of the two discs 30 are spaced apartas shown in FIGURE 4 to define between them a deep annular recess 34whose depth and cross-section correspond to those required in the fin tobe formed.

It will be realised that in FIGURES 1 and 4 the width of the gap 34between the margins of the two discs has been considerably exaggeratedfor the sake of clarity, since in general fins which are much thinner inrelation to their height will be required and accordingly a muchnarrower recess 34 would be used. The milling cutter 31 which isarranged behind the rearmost disc 30 also de-. fines with that disc asecond similar recess 35.

In operation the chuck 21 of the lathe, and with it a workpiece 10, isrotated slowly about its longitudinal axis at a speed of between 14 and100 revolutions per minute, whilst the lathe saddle 36 is slowlytraversed automatically along the length of the workpiece by means of alead screw 37. At the same time the fin-forming tool constituted by thetrain of discs 30 and the milling cutter 31 is advanced into contactwith the surface of the workpiece by transverse movement of thecross-slide 24, whilst the discs 30 are being rotated at high speed, forexample 4500 revolutions per minute, the resultant repeated impactingand friction heating the metal of the workpiece in the region adjacentto the discs to a temperature sulficient to soften the metal, say 400 or500 C. The traversing of the cross-slide 24 causes the spaced edges ofthe discs 30 to bite into the side of the rotating workpiece 10 thesoftened metal of the workpiece being displaced to either side of eachdisc and extruded radially outwardly into the annular recess 34 to forma fin which, due to the longitudinal traverse of the saddle 36, will beprogressively formed as a continuous helical fin 38 of correspondingpitch and of section and height equal to the section and depth of theannular recess 34. Lubricant is continuously directed onto the contactfaces of the discs 30 and of the workpiece 10 through nozzles one ofwhich is visible at 39 in FIGURE 1. To aid in the formation of thehelical fin 33, the axis of the spindle 29 on which the discs 39 aremounted is preferably inclined at a small angle, corresponding to theangle of lead of the helix, so that the planes of the faces of the discs30 will approximately conform to the faces of the helical fin 38 withwhich they are in contact. The opposite faces of each disc 30 in theperipheral region are shown as parallel to one another in FIGURE 4, butin some cases, to facilitate the entry and exit of the discs 35) intothe grooves between successive convolution of the fin 38, and also torelieve friction, the discs may be slightly thicker at their extremeperipheral portions. Alternately, if a fin of tapered crosssection isrequired, the marginal portion of the discs 30 may be themselves taperedin section in the outward direction to define between them a recess 34which is wider at the top than at its bottom.

The purpose of the circular milling cutter 31 which is also mounted onthe spindle 29 behind the two discs 30 is to enter into the helicalgroove formed between successive convolutions of the helical fin 38 andto trim the base of the groove accurately to the required square orother section, as determined by the shape of the edges of the cutterteeth. For this purpose the milling cutter is of approximately the sameradius and thickness as each of the discs 30 and is mounted just behindthe rearmost disc 30 at corresponding axial spacing from it.

There is thus formed on a tubular or bar workpiece a continuous helicalfin of extremely accurate dimensions the fin being formed extremelyrapidly by a process similar to extrusion which produces no scrap metalat all except for the trivial quantity due to the trimming action of themilling cutter 31. It will also be observed from FIGURE 2 that theperipheral radius of the formed fin is greater than the original radiusof the workpiece 10 itself whilst the thickness of the fin may be verysmall. Thus on a bar or tube of magnesium-beryllium alloy originally 1%inches in diameter a fin /2 inch deep and only a few thousandths of aninch in thickness can readily be formed.

It is preferred that the discs 30 and the workpiece 10 should be rotatedin opposite directions, although since the speed of rotation of theworkpiece is very small in comparison with that of the discs it would bealmost equally satisfactory for the two to be rotated in the samedirection, since the relative angular velocity between them will not begreatly different in the two cases. A suitable speed of rotation of theworkpiece is 72 revolutions per minute, which can be producedconveniently on a screw-cutting 1athe To start the fin formation therotating discs are merely advanced into contact with the cylindricalsurface of the workpiece at one end and are pressed inwardly as themetal heats and softens. It is not necessary to provide a tapered endportion on the workpiece for leading the discs into the workpiece.

The arrangement described, using the train of two discs 30 asillustrated in FIGURE 4, produces a single helical fin. If acircumferential fin is required this can of course be produced byremoving the milling cutter 31 and advancing the discs into the flank ofthe rotating workpiece without rotating the lead screw 37, so that thereis no axial movement of the discs relatively to the workpiece. The axisof the spindle 29 should preferably be made parallel to the axis of theworkpiece for this operation. By employing a larger number than two ofthe discs 30, all arranged side by side on the common spindle 29, acorrespondingly increased number of circumferential fins can be formedsimultaneously. Thus if n discs are provided, n1 fins will be formedsimultaneously.

As already mentioned, the fin formation effected by the rapidly rotatingdiscs constitutes a process of displacement or extrusion of the metal ofthe workpiece into the annular recesses between the discs, the metalhaving become heated and softened by the engagement of the discs withthe workpiece. The discs themselves may have many diflerent profilesbesides that illustrated in FIGURE 3, and with workpieces of certainmetals it is even possible to form small fins by this process usingcircular discs Whose edges are perfectly smooth, the friction betweenthe smooth edges of the discs and the workpiece sufiicing to heat andsoften the metal suificiently for displacement radially outwardlybetween the discs. However the radial height of fins which can be formedwith smooth discs is very limited and the process is slow.

Much higher fins can be formed, and at greater speed, if the edges ofthe discs are formed with suitable undulations, projections, or othersuitable variations in height affording blunt leading edge portionswhich are inclined rearwardly and outwardly to their circular path oftravel, to provide a succession of impact on the workpiece, the hammereffect of which greatly assists in the local heating and softening ofthe metal and in its displacement into fin form. Thus in FIGURE 3, eachdisc is formed with a smooth symmetrical peripheral undulation Certainother suitable forms of disc profile are illustrated in FIGURES 5A to5D.

In FIGURE 5A, each disc is formed with a series of discontinuous lugs 50protruding from the otherwise circular periphery 51. The lugs 50 aresymmetrical and have smoothly curved rearwardly inclined leading edges52, flattened tops 53, and rear edges 54 which are the mirror images ofthe leading edges. Like those of FIG- URE 3, the discs shown in FIGURE5A being symmetrical in profile are reversible in operation, so thattheir useful life is correspondingly increased.

In FIGURE SE a disc 55 is shown which has but a single protruding lug 56of the same pattern as the lugs 50 of FIGURE 5A, the remainder of thecircumferential edge of the disc 55 being circular and smooth.

In FIGURE 5C a disc 58 is shown which is formed with protrusions 59 ofgenerally unsymmetrical form, each protruding lug or tooth 59 having agently inclined leading edge 60 leading over a rounded tip 61 to atrailing edge 62 which is steeply cut away or may even be undercut. Thedisc 58 is therefore unidirectional. In practice the discs 58 maycomprise conventional milling cutters the tips of the teeth of whichhave been ground down to smoothly rounded form, and these cutters willbe rotated in the reverse direction to that employed for milling so thatthe backs of the teeth constitute the rearwardly inclined leading edgeswhich first strike the metal of the workpiece.

Another possible form of disc is illustrated in FIGURE 7 5D in which theedge of a circular disc 63 is formed with four flats or chords 64 spaceduniformly around its periphery the corners afforded by the adjacent endsof adjacent flats 64 constitute the necessary impact portions whoseleading edges strike the workpiece with a hammer effect.

Many other forms of disc profile suitable for producing an impact effecton the workpiece may be conceived, to provide one or more impactportions each affording rearwardly and outwardly inclined smooth leadingedges to strike the work and heat and plasticise the metal, the leadingedge being followed up by a trailing portion or lug of greater radialheight which is dragged through the pasticised metal forming a grooveand displacing the metal sideways. The displaced metal between twoadjacent discs is then extruded between them into fin form, the sidefaces of the trailing portions of the adjacent impact portions of thediscs serving to shape and steady the newly extruded fin until it hascooled sufficiently to be self-supporting. The process may thus bedescribed as a form of rotary impact extrusion of a fin, and asmentioned above it enables fins of greater height to be formed than ispossible using plain-edged discs.

In the second embodiment of the invention illustrated in FIGURE 6 thegeneral arrangement of the capstan lathe 13 and of the supportingstructure 25 mounted on the carriage as of the lathe is as before, andsimilar parts are given the same reference numerals. In this case,however, a longitudinal fin 76 is required to be formed on the workpieceIii parellel to its axis, and accordingly the spindle 29 which carriesthe two discs 30 is arranged with its axis and that of the discstransverse to the axis of the workpiece, the spindle being driven asbefore by means of the motor 26 through the belt drive 32 but the motoraxis being at right angles to that employed in the embodiment ofFIGURE 1. Since the fin '76 is required to be longitudinal, theworkpiece must not rotate during fin formation and accordingly it issupported by a block 72 mounted on the base of the ructure 25. Moreover,since the chuck 21 will usually rotate when the carriage 36 of the latheis moved, a roller race 73 is interposed between a centerpiece 74spigoted into the end of the workpiece It) and the chuck 21 of thelathe. At the tail stock end, the turned-down end 15 of the workpiece issupported directly by a tool holder 75 secured to the turret of thelathe, no ball race being required at that end.

The two discs 3t mounted on the spindle 29 may be of the undulating typeillustrated in FIGURE 3 or of any the other types shown in FIGURES 5A to5D. No milling cutter is provided however in association with the discs,which are disposed with their general planes symmetrically located oneither side of the vertical plane through the axis of the workpiece. Inoperation, as previously, the discs are advanced into engagement withthe upper part of the workpiece at one end, so as to heat and plasticisethe metal locally by the friction and impacting of the undulating edgesof the discs. The lathe carriage 36 is slowly traversed along the lengthof the workpiece, so that a single longitudinal fin 7% is extrudedbetween the two rapidly rotating discs 39 as the carriage 36 advancesalong the workpiece. The fin may be formed completely from end to end ofthe workpiece, and it is not necessary to provide a tapered lead-inportion at either end of the workpiece, as the discs are simply advancedinto engagement with the square edge of the end of the workpiece tostart the fin formation.

If a number of longitudinal fins is requ red to be formed at spacedintervals around the circumference of the Workpiece, succession ofpasses along the length of the workpiece by the discs 39 can be made,the workpiece being rotated through a suitable angle about its axisbetween successive passes.

In the embodiment illustrated in FIGURES 7 to 9, the general principleof fin formation by the application of a rapidly moving pair of spacededges to the workpiece is employed as in the previous embodiments, butin this case the edges instead of being constituted by the outside edgesof a number of coaxial discs are constituted by the inside edges of anumber of coaxial rings 30 surrounding the workpiece.

Thus a pair of rings formed with internal, generally circular edgeportions 81 of reduced axial thickness, is mounted, together with amilling cutter 82 of the ring type of the same general dimensions, in astack bounded by a suitable number of packing rings 83 serving toincrease the axial length of the stack to a convenient size. The stackis clamped together by means of bolts 84 between flanged end rings 85having flanges 86 so as to form a drum into whose interior protrude theperipheral portions 81 of the rings 80, and the teeth of the millingcutter 82. The drum is mounted for rotation within roller races 93 whichare supported by the sides of nonrotating pegs 87 protruding inwardlyfrom the side walls 88 of a supporting bridge 89 secured to a base plate99, which is mounted on the cross-slide of the lathe carriage 36 formovement transversely to the workpiece 10. The drum constituted by thestack of rings 80, 82 and 83 and 85 is thus rotatably mounted within thebridge 89 and is driven at a high speed of rotation about the axis ofthe rings 80 by a belt drive 91 from an electric motor 92 mounted on thebase plate 90 to one side of the bridge 89.

The workpiece 10, which is mounted as in the embodiment of FIGURE 1between the head stock and tail stock of the lathe for rotation with thechuck, extends through the rings 80, 82, 83, and 85 so that by suitabletransverse movement of the cross slides of the lathes the inwardlyprojecting edge portions 81 of the rapidly rotating rings 80 can bepressed into contact with the side of the workpiece, whilst the latteris being rotated by the chuck and whilst the rings 80 are beingtraversed slowly along the length of the workpiece by the longitudinalmovement of the carriage 36 affected by the lead screw 37. There is thusformed on the workpiece 10 an external helical screw thread 94 by aprocess which is precisely analogous with that employing the discs 38 asdescribed in relation to FIGURE 1, save only that in the present caseinternal edges of the rings 80 which surround the workpiece are used tosoften the metal and to displace it radially outwardly into helical finform.

The internal diameters of the rings 80 and of the milling cutter 82 mustclearly be considerably larger than the external diameter of theworkpiece, and in practice the internal diameter of the ring edges willusually be at least twice the original external diameter of theworkpiece 10. As before, the edges of the inwardly protruding marginalportions 81 of the rings 80 are all formed with a suitable pattern ofradial undulations or protrusions, in this case constituting theconverse of the unsymmetrical tooth arrangement of the disc 58 shown inFIGURE C. Thus as shown in FIGURE 8 the internal edge of each disc 80 isformed with a series of radial inwardly protruding lugs or teeth 95,each providing a rearwardly and inwardly inclined leading edge 96 and amore steeply inclined trailing edge 97, separated by a smoothly roundedtip 98.

The embodiment of FIGURES '7 to 9 using rotating rings which surroundthe workpiece for the purpose of forming an extruded external fin aroundthe workpiece, can of course be used equally for the formation ofcircumferential fins as for the formation of a helical fin, and in bothcases two or more fins may be formed simultaneously by the use of asuitable number of the rings 80. Moreover this embodiment has theadvantage that the bearing arrangements for supporting the rapidlyrotating rings 80 may be made very much larger and more substantial thanis convenient in cases where rotating discs are used, so that thesehearings will be able to stand up to much greater bearing pressures dueto the reaction of the workpiece during fin formation. This in turnenables the apparatus to be used for fin formation on tougher metals oralloys or those having relatively high melting points, for examplecopper or steel or other ductile or malleable metals. For example it isenvisaged that for fin formation on a steel workpiece it will probablybe essential to use an arrangement of rings such as the rings 80 insteadof discs for forming the fins, simply on account of the more robustbearing means which can thereby be provided.

In all the specific embodiments which have been described andillustrated, a tubular workpiece has been employed. It is found incertain instances that where discs or rings having undulating orirregular edges are used to provide an impact effect on the metal or theworkpiece to assist the fin formation, small internal circumferentialridges may be formed thereby within the bore of the tubular workpiece.If such internal ridges cannot be tolerated and an accurate smooth-boredend product is required, the formation of such ridges may be preventedby the insertion of a solid close-fitting mandrel within the bore of thetubular workpiece. Moreover the various apparatus described can equallybe used of course for fin formation on solid cylindrical bar stockinstead of on tubular stock.

Whilst the workpiece-en gaging rotary edges of the tool in the variousspecific embodiments have been described and illustrated as being in theform of separate discs or rings, it will be clear that the tool mightequally take the form of a cylindrical hub or drum formed with a seriesof spaced coaxial integral annular fianges protruding either outwardlyor inwardly as the case may be.

Again, the tool might also take the form of a suitable chain or striprotated around pulleys or sprockets and pressed into engagement with theworkpiece. For example a bandsaw having suitable rounded teeth, drivenin the reverse direction to that employed for cutting, might beemployed.

What we claim as our invention and desire to secure by Letters Patentis:

1. The method of forming an integral fin on the surface of a workpiecemade of a material which becomes softened and capable of extrusion whenheated, compris ing the steps of: progressively and simultaneouslyapplying to the surface of the workpiece along relatively spacedparallel paths, extending along the opposite sides of the intendedlocation of the fin, and at locations maintained substantially abreastof each other along said paths, rapid successions of impacts directedgenerally normally to said surface, to locally heat and extrude materialfrom the said parallel paths into the space between said paths to formsaid fins, and during the extrusion and thereafter for a predeterminedperiod, continuously confining and supporting a portion of the extrudedmaterial between substantially parallel planes generally normal to saidsurface and coincident with the relatively adjacent edges of said paths.

2. The process of forming an integral fin on the cylindrical surface ofa workpiece made of a material capable of extrusion, comprising thesteps of: progressively and simultaneously applying to said cylindricalsurface along relatively uniformly spaced paths extending helicallyaround said surface, rapid successions of generally radial impacts, toindent said surface along said paths and extrude at least part of thedisplaced material into the space between said paths and during theextrusion and thereafter for a predetermined period, continuouslyconfining and supporting a portion of the extruded material within aspace having the cross-sectional configuration desired in the said fin.

References Cited in the file of this patent UNITED STATES PATENTS 80,022Shefiield July 14, 1868 1,840,641 Short Jan. 12, 1932 1,909,005 PaughMay 16, 1933 2,170,513 Asbeck Aug. 22, 1939 2,188,456 Galber Jan. 30,1940 2,306,827 Mohan Dec. 29, 1942 2,402,209 Ryder June 18, 19462,562,785 Hill July 31, 1951 2,586,011 Doelter Feb. 19, 1952 2,661,526Bruegger Dec. 8, 1953 2,680,975 Goldsmith June 15, 1954 2,715,846 GrobAug. 23, 1955 2,779,223 Schustcr Jan. 29, 1957 2,807,971 Garner et alOct. 1, 1957

1. THE METHOD OF FORMING AN INTEGRAL FIN ON THE SURFACE OF A WORKPIECEMADE OF A MATERIAL WHICH BECOMES SOFTENED AND CAPABLE OF EXTRUSION WHENHEATED, COMPRISING THE STEPS OF: PROGRESSIVELY AND SIMULTANEOUSLYAPPLYING TO THE SURFACE OF THE WORKPIECE ALONG RELATIVELY SPACEDPARALLEL PATHS, EXTENDING ALONG THE OPPOSITE SIDES OF THE INTENDEDLOCATION OF THE FIN, AND AT LOCATIONS MAINTAINED SUBSTANTIALLY ABREASTOF EACH OTHER ALONG SAID PATHS, RAPID SUCCESSIONS OF IMPACTS DIRECTEDGENERALLY NORMALLY TO SAID SURFACE, TO LOCALLY HEAT AND EXTRUDE MATERIALFROM THE SAID PARALLEL PATHS INTO THE SPACE BETWEEN SAID PATHS TO FORMSAID FINS, AND DURING THE EXTRUSION AND THEREAFTER FOR A PREDETERMINEDPERIOD, CONTINUOUSLY CONFINING AND SUPPORTING A PORTION OF THE EXTRUDEDMATERIAL BETWEEN SUBSTANTIALLY PARALLEL PLANES GENERALLY NORMAL TO SAIDSURFACE AND COINCIDENT WITH THE RELATIVELY ADJACENT EDGES OF SAID PATHS.